Satellites are becoming important links for communication between stations at different locations throughout the world, particularly for mobile communication stations. For a satellite system to give worldwide coverage, a network or constellation of satellites is desirable. The minimum number of satellites and their orbital requirements to achieve continuous single or multiple coverage on various parts of the earth have been described in The Journal of the Astronautical Science, for example, "Analytic Design of Satellite Constellations for Zonal Earth Coverage Using Inclined Circular Orbits" by L. Rider, VOL 34. No. 1 January-March 1986, pp. 31-64, and "Circular Polar Constellations Providing Continuous Single or Multiple Coverage Above a Specified Latitude" by W. S. Adams and L. Rider, Vol 35, No. 2 April-June 1987, pp. 155-192.
Each satellite within such a satellite constellation has one or more directional antennas producing a coverage pattern on earth referred to as the "foot-print" of the satellite antenna. When multiple polar orbiting satellites are used, the satellites converge towards the poles and antenna footprints begin to overlap.
In the past overlap of antenna patterns has often been desired (see for example, Adams and Rider, supra). But, where the antenna footprint is made up of separate "cells" in which individual communication is to take place, overlap may not be desirable. When cells from one satellite overlap cells from another satellite, there is redundancy of coverage and potential communication interference. Thus, there is an ongoing need to avoid such interference problems in multi-satellite cellular systems.
As used herein, the term "satellite" is meant to include any satellite moving relative to another satellite. Non-limiting examples are, multiple satellites which converge during orbit or one or more satellites moving relative to a geostationary satellite. The term "cell" is intended to refer to one or more portions of an antenna pattern in which communication may occur independent of communications in other portions (i.e., other cells) of the antenna pattern